At present, the commonly-used energy storage device is lithium ion battery, which is featured by a carbon material-made cathode and a lithium-containing compound-made anode. When this lithium ion battery is under charging, its anode material generates lithium ions that move to the cathode through electrolyte. Carbon serving as the cathode is of a layered structure with a large number of micropores therein, so those lithium ions that reach the cathode are embedded into the micropores of the carbon layer. The more the lithium ions are embedded, the higher the charging capacity will be; when the lithium ion battery is under discharging, the lithium ions embedded in the cathode carbon layer move out and then back to the anode. The more the lithium ions move back to the anode, the higher the discharging capacity will be. While performance, safety and other factors of the lithium ion battery have been dramatically improved after constant improvement on the lithium ion battery in this industry, there are still a few major shortcomings in the lithium ion battery owing to limitations from its basic structure and charging/discharging principle:
1. Small Power Density of the Lithium Ions. Limited by the electrode energy storage principle and electrolyte structure of the lithium ion battery, the lithium ion battery only has a power density of 1 kw/kg, which places restrictions on application of the lithium ion battery in the aspect of power battery.
2. Small Energy Density of the Lithium Ions. The lithium ion battery has an energy density of 120-160 Wh/kg, and this cannot completely meet the demand in power applications, such as electric vehicle.
3. Long Charging Time. The lithium ion battery needs to be charged for over 2-4 hours in case of a charging current of 0.5 C-1 C. In case of a high current of more than 2 C, the charging time can be reduced, but this high current could separate out hydrogen and oxygen from the electrolyte of the lithium ion battery, and simultaneously, high temperature is created to result in the hidden safety trouble of explosion of the lithium ions. Meanwhile, this high current will cause damage to the microstructures of the anode and cathode of the lithium ion battery, which reduces the energy storage capacity and shortens the service life to a large extent.
4. Short Cycle Life. In the event of deep discharging, the charging/discharging cycle life of the lithium ion battery is approximately from 300 times to 500 times, leading to short service life.
5. Limited Service Temperature Range. The service temperature range of the lithium ion battery is from minus 20° C. to 60° C., use of the lithium ion battery at a temperature higher than the temperature range reduces energy efficiency, causes damage to the battery and possibly leads to explosion. And use of the lithium ion battery at a temperature lower than the temperature range reduces the efficiency and energy storage capacity of the battery significantly.
Thus, a technical problem that needs to be solved urgently in this industry is how to provide a novel electrostatic energy storage device with high energy density and high power density, and a preparation method thereof.